Cam phasers for internal combustion engines are well known. In a typical cam phaser a locking bolt that is adjustable in a controlled manner is arranged with a sliding fit in a bore hole in a rotor blade of the cam phaser in order to block the rotor from rotating relative to the stator under particular operating conditions of the cam phaser and of the engine. A known locking device includes a locking bolt and a reset spring which loads the bolt in a hardened support, so that the rotor is locked relative to a stator that is fixed relative to the cog wheel or the sprocket.
Typically the locking device is unlocked by loading the locking bolt with a hydraulic pressure which corresponds to a pressure in a pressure cavity. The locking is performed by the reset spring, subsequently designated as preload element. This means that the hydraulic pressure of the pressure cavity has to cause a resulting force on the locking bolt, wherein the resulting force is greater than a spring force of the preload element which is typically provided as a coil spring. On the other hand side the spring force has to be greater than the resulting force of the hydraulic pressure in order to provide safe locking.
The resulting force of the hydraulic pressure is a function of a viscosity of the hydraulic fluid, of corresponding channels through which the hydraulic fluid runs for loading the locking bolt and of a configuration of the hydraulic valve of the cam phaser and a configuration of a hydraulic valve of the cam phaser through which the pressure chambers are hydraulically loaded. Thus, it can occur that a resulting torsion torque reaches spike values in applications with high cam shaft speeds which can lead to unlocking since the pressure from the pressure cavity which is provided for unlocking increases.